Man Is Paving His Own Road To Extinction

January 07, 1996|By EVALYNE C. ROBINSON Book Reviewer

"To a paleontologist, death is a fact of life and extinction is a fact of evolution. Some 30 billion species are estimated to have lived since multicellular creatures first evolved [530 million years ago] in the Cambrian explosion. According to some estimates, 30 million species populate today's Earth. This means that 99 percent of all species populate today's Earth. This means that 99.9 percent of all species that have ever lived are extinct. Life's grip on Earth is evidently more precarious than we might like to accept."

The foregoing statement identifies the thesis of "The Sixth Extinction," in which the fact and cause of these extinctions are discussed.

Although written in an easily read style, "The Sixth Extinction" is a thoroughly scientific account derived from man's existence on Earth and man's devastating end early in the next century that the authors predict will come if we continue to destroy the environment at the rate we do today.

"Home sapiens," they warn, "as the most dominant group on Earth, are the engineers of the sixth extinction."

Their focus in this work is on man's responsiblity and obligation.

Richard Leakey and Roger Lewin identify five greqt periods of mass extinction in the history of life on Earth. These were Biotic crises in which at least 65 percent of the Earth's marine animal species became extinct in a brief geological instant - catastrophic events in which "global biology had an extremely close brush with total distruction."

Leakey and Lewin present scientific data to support that the sixth great extinction, when as much as 50 percent of the Earth's species may disappear, is underway and is following an accelerating pattern consistent with the previousufive extinctions - "30,000 species are wiped out by human agency every year."

Humans endanger the existence of species in many ways. Three are outstanding"

* Direct exploitation (hunting, collecting, eating).

* Biological havoc (the introduction of alien species to new ecosystems).

* And, most important, the destruction and fragmentation of habitat, especially the tropical rainforests, resulting from, among other causes, the continued growth of human population, the expansion of agricultural land, and the building of towns and cities.

In the book's final chapter, Leakey and Lewin stress why Homo sapiens, as the rational species, must gain insight into the working balances in the natural world, why it is necessary that these balances be sustained, and why it is important to understand man's vulnerable place in The Great Chain of Being, Unrestrained, the authors warn, Homo sapiens might not only be the agent of the sixth extinction, but also one of its victims."